Method of forming high density, high shorting margin, and low capacitance interconnects by alternating recessed trenches

ABSTRACT

Embodiments of the invention describe low capacitance interconnect structures for semiconductor devices and methods for manufacturing such devices. According to an embodiment of the invention, a low capacitance interconnect structure comprises an interlayer dielectric (ILD). First and second interconnect lines are disposed in the ILD in an alternating pattern. The top surfaces of the first interconnect lines may be recessed below the top surfaces of the second interconnect lines. Increases in the recess of the first interconnect lines decreases the line-to-line capacitance between neighboring interconnects. Further embodiments include utilizing different dielectric materials as etching caps above the first and second interconnect lines. The different materials may have a high selectivity over each other during an etching process. Accordingly, the alignment budget for contacts to individual interconnect lines is increased.

FIELD OF THE INVENTION

Embodiments of the present invention relate generally to the manufactureof semiconductor devices. In particular, embodiments of the presentinvention relate to low capacitance interconnect structures forsemiconductor devices and methods for manufacturing such devices.

BACKGROUND AND RELATED ARTS

As microprocessors become faster and smaller, integrated circuitry (IC)becomes more complex and components become more densely packed.Interconnect lines are needed to provide electrical connections todifferent portions of the device. The current patterning technique forforming interconnect lines includes the formation of trenches that havea uniform depth, as shown in FIG. 1. Conductive material is thendisposed into the trenches to form interconnect lines 120. However, asthe pitch of the interconnect lines decrease, increases in theline-to-line capacitances between neighboring interconnect lines becomesa limiting factor. Prior attempts to decrease the line-to-linecapacitance rely on low-k dielectric materials and techniques such asusing air pockets. However, these approaches are limited by materialproperties and generally result in poor structural integrity.

In addition to the increase in the line-to-line capacitance, shrinkingthe pitch of the interconnect lines increases the demands on masking andetching processes required for the formation of connections to theinterconnect lines from subsequent layers. In FIG. 1, a contact mask 160is disposed over the etch stop layer 105. In order to make a contact toa single interconnect line 120, the contact mask 160 must be patternedto have a mask opening M that is aligned over a single interconnect line120. If the mask opening M is misaligned and extends over a neighboringinterconnect line 120, as shown in FIG. 1, then the etching processwould provide contacts to both interconnect lines, thereby preventingthe formation of an isolated connection. Accordingly, reducing the pitchof the interconnect lines requires aligning and patterning contact maskswith increased precision that may not be obtainable with conventionallithography processes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an interconnect structure according to the prior art.

FIGS. 2A-2E illustrate cross-sectional views of an interconnectstructure according to embodiments of the invention.

FIG. 3 illustrates a graph of the line-to-line capacitance with respectto the recess depth of alternating interconnect lines according toembodiments of the invention.

FIGS. 4A-4Q illustrate a processing flow for forming low capacitanceinterconnect structures according to embodiments of the invention.

FIGS. 5A-5F illustrate a processing flow for forming low capacitanceinterconnect structures according to embodiments of the invention.

FIG. 6 illustrates a schematic diagram of a computing device thatutilizes a low capacitance interconnect structure in accordance with anembodiment of the invention

DETAILED DESCRIPTION

Embodiments of the invention are directed towards an interconnectstructure with reduced line-to-line capacitance and methods of makingsuch devices. In order to reduce the line-to-line capacitance in aninterconnect structure, the effective distance between neighboringinterconnect lines is increased. Embodiments of the invention increasethe effective distance between neighboring interconnect lines byrecessing alternating lines. Embodiments of the invention include firstinterconnect lines that are recessed into an interlayer dielectric suchthat their top surfaces are disposed below the top surfaces ofneighboring second interconnect lines. According to additionalembodiments, the first interconnect lines are recessed into theinterlayer dielectric such that their top surfaces are disposed belowthe bottom surfaces of neighboring second interconnect lines. Thedecrease in line-to-line capacitance is strongly proportional toincreases in the recess depth of the first interconnect lines.Accordingly, reductions in the line-to-line capacitance made inaccordance with embodiments of the present invention are not solelydependent on the dielectric constant of the materials used for theinterlayer dielectric. As such, embodiments of the invention may utilizedielectric materials that have higher dielectric constants relative tothe prior art without increasing the line-to-line capacitance.

According to an embodiment of the invention, a first trench etchingprocess is used to form the trenches in which the first interconnectlines are formed, and a second trench etching process is used to formthe trenches in which the second interconnect lines are formed. Etchingalternating trenches with separate etching processes allows for theinterconnect lines to be formed in trenches that are different depths,as opposed to being formed in trenches of uniform depth, as shown inFIG. 1. Therefore, the first interconnect lines may be recessed belowthe second interconnect lines, thereby reducing the line-to-linecapacitance in the interconnect structure.

Additional embodiments of the invention also utilize two differentdielectric materials for the first and second dielectric caps.Embodiments include an interconnect structure with first dielectric capsthat have a high selectivity over the second dielectric caps during anetching process. Additional embodiments further include first and seconddielectric caps made from materials that both have a high selectivityover an etch-stop layer formed above the interlayer dielectric during anetching process. The use of materials that have high selectivity overeach other during an etching process allows for the formation of contactopenings that are more forgiving to misalignment. Since an etchant maybe chosen that selectively removes only one of the materials, the maskopening may span across more than one interconnect line, therebyproviding a large misalignment budget.

FIG. 2A illustrates a low capacitance interconnect structure 100according to an embodiment of the invention. The interconnect structure100 may be used in conjunction with any semiconductor device thatutilizes multi-level interconnects, such as an IC circuit and the like.Interconnect structure 100 is formed in an interlayer dielectric (ILD)103. Embodiments of the invention utilize low-k dielectric materialsthat are typically known in the art for use as ILDs such as, silicondioxide. According to embodiments of the invention, low-k dielectricmaterials suitable for formation of the ILD 103 may also include, butare not limited to, materials such as carbon doped silicon dioxide,porous silicon dioxide, or silicon nitrides. Additional embodiments ofthe invention may include the ILD 103 formed from dielectric materialswith k-values less than 5. Embodiments may also include an ILD with ak-value less than 2. According to additional embodiments, the ILD 103may include air gaps and have a k-value of 1. According to embodimentsof the invention, ILD 103 may be less than 100 nm thick. According toadditional embodiments, the ILD 103 may be less than 40 nm thick. Anadditional embodiment of the invention may further include an ILD 103with a thickness between 40 nm and 80 nm. Additional embodiments includean ILD 103 that is approximately 60 nm thick.

In an embodiment, an etch-stop layer 105, such as a nitride or an oxide,is disposed over the top surface of the ILD 103. According to anembodiment, etch-stop layer 105 is resistant to an etchant that may beused to etch through an additional layer 180, such as an additionalinterconnect layer, that may be disposed above the etch-stop layer 105.Embodiments of the invention include an etch-stop layer 105 that isbetween 3 nm and 10 nm thick. According to an embodiment, the lowcapacitance interconnect structure 100 may also have a bottom etch-stoplayer 101, such as a nitride or an oxide material, disposed below theILD 103. The lower etch-stop layer 101 may separate the ILD 103 fromother interconnect structures or the active circuitry of a semiconductordevice, such as layer 170. According to an embodiment, bottom etch-stoplayer 101 is resistant to an etchant that may be used to etch throughthe ILD 103. Embodiments of the invention include a bottom etch-stoplayer 101 that is between 3 nm and 10 nm thick.

According to an embodiment, interconnect structure 100 includes firstand second interconnect lines 121, 122 disposed into the ILD 103 in analternating pattern, as shown in FIG. 2A. According to an embodiment thealternating pattern includes a first interconnect line 121 bordered oneach side by second interconnect lines 122. According to embodiments ofthe invention, the first and second interconnect lines 121, 122 areformed with conductive materials. By way of example, and not by way oflimitation the conductive materials used to form the interconnect linesmay include, Cu, Co, W, NiSi, TiN, Mo, Ni, Ru, Au, Ag, or Pt. Accordingto an embodiment, the same metal is used to form both the first andsecond interconnect lines 121, 122. According to an alternativeembodiment, the first and second interconnect lines 121, 122 are formedwith different metals. The interconnect lines 121, 122 are spaced apartfrom each other by a pitch P. Embodiments of the invention include highdensity interconnect lines with a pitch P less than 60 nm. Furtherembodiments of the invention include a pitch P that is less than 30 nm.Embodiments of the invention include interconnect line widths W lessthan 30 nm. Additional embodiments of the invention include interconnectline widths W less than 15 nm. While the width W of the first and secondinterconnect lines 121, 122 are shown as being substantially equal inFIG. 2A, additional embodiments are not so limited. As such, furtherembodiments of the invention include first interconnect lines 121 thathave a width W that is larger than or smaller than the width W of thesecond interconnect lines 122.

As shown in FIG. 2A, the top surfaces 151 of the first interconnectlines 121 are recessed a distance R into the ILD 103. According toembodiments of the invention, R is chosen such that the top surfaces 151of the first interconnect lines 121 are disposed at substantially thesame depth as the bottom surfaces 153 of the second interconnect lines122, as shown in FIG. 2A. In additional embodiments of the invention, Ris chosen such that the top surfaces 151 of the first interconnect lines121 are formed between the top surfaces 152 and bottom surfaces 153 ofthe second interconnect lines 122, as shown in FIG. 2B. An arrangementaccording to this embodiment may be desirable when the thickness of theILD 103 needs to be reduced. In an additional embodiment of theinvention, R is chosen such that the top surfaces 151 of the firstinterconnect lines 121 are formed below the bottom surfaces 153 of thesecond interconnect lines 122, as shown in FIG. 2C. According toadditional embodiments, the top surfaces 152 of the second interconnectlines 122 are also recessed into the ILD 103.

Referring back to FIG. 2A, embodiments of the invention include firstinterconnect lines 121 that are a height H₁ and second interconnectlines 122 have a height H₂. Embodiments of the invention includeinterconnect structures 100 where H₁ and H₂ are chosen to be the sameheight, as shown in FIG. 2A. According to additional embodiments,interconnect structure 100 includes first and second interconnect linesthat have heights H₁ and H₂ that are not the same, as shown in FIG. 2B.While H₁ is shown in FIG. 2B as being larger than H₂, embodiments of theinvention are not so limited. Alternative embodiments includeinterconnect structures 100 in which H₁ is smaller than H₂, as shown inFIG. 2C. According to embodiments of the invention, the first and secondheights H₁ and H₂ are between 10 nm and 30 nm According to an additionalembodiment of the invention H₁ is approximately 24 nm and H₂ isapproximately 16 nm.

Referring now to FIG. 3, a graph of the relationship between reductionin the line-to-line capacitance and the depth of the recess R of thefirst interconnect lines 121 into the ILD 103 according to variousembodiments of the invention is shown. The y-axis is a measurement ofthe reduction in the line-to-line capacitance (as a percent of theline-to-line capacitance of the prior art device depicted in FIG. 1),and the x-axis is the recess depth R (in nanometers) of the top surface151 of the first interconnect lines 121. The box 351 is a referencemarker of the line-to-line capacitance of the prior art device shown inFIG. 1. Box 351 therefore represents a device in which all interconnectlines 120 are formed at the same depth. The devices measured in FIG. 3include second interconnect lines 122 that have a height H₂ ofapproximately 16 nm. Accordingly, marker 350 is the measurement wherethe top surfaces 151 of the first interconnect lines 121 are recessedcompletely below the bottom surface 153 of the second interconnect lines122, as shown in FIG. 2A. By way of example, marker 350 indicates thatthe line-to-line capacitance may be reduced by approximately 35% whenthe first and second interconnects 121, 122 are completely offset fromeach other, as shown in FIG. 2A. The graph shows the decrease in theline-to-line capacitance is strongly proportional to the value chosenfor the recess R of the first interconnect lines 121 into the ILD 103.

Referring back to FIG. 2A, embodiments of the invention further includea first dielectric cap 125 disposed above the first interconnect lines121. The first dielectric cap 125 fills the remaining portion of thetrench in which the first interconnect lines 121 are formed. Accordingto an embodiment, top surfaces of the first dielectric caps 125 aresubstantially coplanar with the etch-stop layer 105. Embodiments of theinvention further include a second dielectric cap 126 that is disposedabove the second interconnect lines 122. The second dielectric cap 126fills the remaining portion of the trench in which the secondinterconnect lines 121 are formed. According to an embodiment, a topsurface of the second dielectric cap 126 is substantially coplanar withthe etch-stop layer 105. Embodiments of the invention include first andsecond dielectric caps 125, 126 made from materials such asSiO_(x)C_(y)N_(z), non-conductive metal oxides and nitrides, such as,but not limited to, TiO, ZrO, TiAlZrO, AlO, or organic materials.According to an embodiment, the first and second dielectric caps aremade with the same material. According to an additional embodiment,first dielectric caps 125 and second dielectric caps 126 are made fromdifferent materials. According to an embodiment, the first dielectriccaps 125 are made from a material that has a high selectivity over thesecond dielectric caps 126 during an etching process. As used herein,when a first material is stated as having a high selectivity over asecond material, the first material etches at a faster rate than thesecond material during a given etching process. According to anadditional embodiment, the second dielectric caps 126 are made from amaterial that has a high selectivity over the first dielectric caps 125.Additional embodiments of the invention include forming the first andsecond dielectric caps 125, 126 from different materials that both havea high selectivity over the etch stop layer 105 during an etchingprocess.

In addition to reducing the line-to-line capacitance, the interconnectstructure 100 may also provide benefits with respect to formingconnections to individual interconnect lines. As shown in the prior artinterconnect device in FIG. 1, precise alignment of the contact mask 160is necessary because there is no etch selectivity between theneighboring interconnects 120. Therefore, in order to provide aconnection to a single interconnect line, the mask opening M needed tobe aligned over a single interconnect line in order to prevent theneighboring lines from being exposed as well. Accordingly, as the pitchof the interconnect lines continues to shrink, the need for an accuratealignment has become another hurdle to the production of semiconductordevices.

As shown in FIG. 2D, embodiments of the invention allow for theselective removal of the first dielectric cap 125 even though the mask160 was misaligned. The selectivity shown in FIG. 2D is possible madepossible in embodiments of the invention that utilize a material for thefirst dielectric cap 125 that has a high selectivity over the materialused for the second dielectric cap 126 and over the etch-stop layer 105.Accordingly, even when the mask opening M is formed over the firstinterconnect line 121 and the neighboring second interconnect line 122,the first dielectric cap 125 can be selectively etched away to formcontact opening 185 without also etching away the dielectric cap 126disposed over the second interconnect line 122.

Referring now to FIG. 2E, a cross-sectional view of an interconnectdevice 100 according to an additional embodiment is shown. Theinterconnect device 100 in FIG. 2E is substantially similar to the oneshown in FIG. 2A and further includes a first through via 123 and secondthrough via 124. According to embodiments of the invention, the firstand second through vias 123, 124 are integrated into the alternatingpattern of the first and second interconnect lines 121,122. As such, inembodiments of the invention, a first through via 123 is formed where afirst interconnect line 121 would otherwise be formed. Similarly,embodiments include forming a second through via 124 where a secondinterconnect line 122 would otherwise be formed. As shown in FIG. 2E,the first through via is formed between two second interconnect lines122, and the second through via 124 is formed between two firstinterconnect lines 121. First through vias 123 are substantially similarto the first interconnect lines 121, with the exception that the line isformed all the way through the ILD 103 and the bottom etch-stop layer101. Accordingly, the first through via 123 provides the ability to makean electrical connection through the ILD 103 to the lower level 170. Asshown in FIG. 2E, the electrical connection to the lower level 170 maybe made to a pad 175 on the lower level 170. Pads 175 may be conductivelines, S/D contacts of a transistor device, or any other feature of asemiconductor device that requires an electrical connection, such as anyregion of 170 that is a portion of the interconnect scheme. Likewise,second through vias 124 are substantially similar to the secondinterconnect lines 122, with the exception that the line is formed allthe way through the ILD 103 and the bottom etch-stop layer 101.Accordingly, the second through via 124 provides the ability to make anelectrical connection through the ILD 103 to the lower level 170. Thoseskilled in the art will recognize that the through vias 123 and 124 neednot extend along the entire length of an interconnect line (i.e., alongthe length of the line extending out of the plane of paper).

Embodiments of the invention further include first and second dielectriccaps 125, 126 disposed above the first and second through vias 123, 124that are substantially similar to those described above with respect tothe dielectric caps disposed above the first and second interconnectlines 121, 122. Accordingly, embodiments allow for a mask opening M thatis formed over the neighboring interconnect lines when a contact needsto be made to a through via, because of the etch selectivity between thefirst dielectric caps 125 and the second dielectric caps 126.

Certain embodiments of the invention may be manufactured according tothe processes described with respect to FIGS. 4A-4Q. Referring now toFIG. 4A, the ILD 103 in which the interconnect structure will be formedis shown. According to embodiments of the invention, a masking stack 400is disposed above the ILD 103. According to embodiments of theinvention, the masking stack 400 comprises multiple layers suitable formasking and etching features into the ILD 103. According to anembodiment, the masking stack 400 may comprise an etch-stop layer 105,such as a nitride or an oxide material, disposed over the ILD 103.Masking stack 400 may further comprise a carbon hardmask 107 that isdisposed above the etch-stop layer 105. The carbon hardmask 107 may beany material suitable for the formation of a hardmask layer, such as anamorphous silicon or a silicon carbide. A hardmask etch-stop layer 110may be disposed above the carbon hardmask 107. According to embodimentsof the invention, the hardmask etch-stop layer 110 may be an etchresistant material, such as, but not limited to TiO, ZrO, MN, ZrAlTiO,or AlO. Masking stack 400 may also comprise a dummy hardmask layer 111that is disposed above the hardmask etch-stop layer 110. According to anembodiment of the invention, the dummy hardmask layer 111 may be anymaterial suitable for the formation of a hardmask layer, such as anamorphous silicon or a silicon carbide. According to an embodiment, themasking stack 400 may further comprise an antireflective layer 112, suchas a silicon layer, disposed above the dummy hardmask layer 111. Theantireflective layer 112 may be included in the masking stack 400 inorder to provide better control of patterning of the mask layer 133disposed above the antireflective layer 112. According to embodiments ofthe invention, the mask layer 133 may be a material typically patternedwith a lithographic process, such as a photo-sensitive resist. As shownin FIG. 4A, the mask layer 133 has been patterned to form the desiredshape for a first structure that will be transferred into the dummyhardmask layer 111. According to embodiments of the invention the ILD103 may be disposed over an additional layer 170. According toembodiments, layer 170 may be an additional interconnect structure or itmay be a device substrate on which electrical circuitry is disposed. Asshown in FIG. 4A, two separate pads 175 are disposed in layer 170. Byway of example, and not by way of limitation, pads 175 may be conductivelines, S/D contacts of a transistor device, or any other feature of asemiconductor device that requires an electrical connection, such as anyregion of 170 that is a portion of the interconnect scheme.

Referring now to FIG. 4B, the pattern of the mask layer 133 has beentransferred into the dummy hardmask layer 111 to form the firstbackbones 115. Embodiments of the invention transfer the pattern of themask layer 133 into the dummy hardmask layer 111 with an etchingprocess, such as wet or dry etching process known in the art. Theremaining portions of the antireflective coating 112 and the mask layer133 have been removed. Next in FIG. 4C, a spacer forming layer 113 isdisposed over the first backbones 115 and the exposed portions of thehardmask etch-stop layer 110. The spacer forming layer 113 may be amaterial typically used for the formation of dielectric spacers, such asan oxide or a nitride. A spacer etching process is then used to form thespacers 114 on each side of the first backbones 115. Embodiments includea spacer etching process that selectively removes the material from thespacer forming layer 113 that is disposed on horizontal surfaces,thereby leaving spacers 114 along the sidewalls of the first backbones115. Subsequent to the spacer formation, the first backbones 115 areetched away, as shown in FIG. 4D.

Referring now to FIG. 4E, the spacers 114 are used as an etch-mask, andtheir pattern is transferred into the hard mask layer 107. After theetching process portions of the hard mask layer 107 and the etch-stoplayer 110 remain, which together will be referred to as the secondbackbone 116. Embodiments utilize etching processes known in the art,such as wet or dry etching process, to transfer the pattern of thespacers 114 into the hard mask layer 107.

Referring now to FIG. 4F, the second backbone 116 is then covered with afilm 108. The film 108 is material that may be used to form a secondspacer material. According to an embodiment, the film 108 may be a hardand conformal material, such as, but not limited to TiO, ZrO, MN, AlO,and combinations thereof. According to an embodiment of the invention,the material used for the second backbone 116 has a high selectivityover the material used for the second film 108 during an etchingprocess. According to such embodiments, the material forming the film108 is resistant to an etching process that will readily etch away thebackbone 116. By way of example, when the second backbones 116 are madefrom an amorphous silicon, then film 108 may be made with titaniumoxide.

Referring now to FIG. 4G, a spacer etching process has been performed inorder to turn film 108 into spacers 109. Embodiments include ananisotropic spacer etching process that selectively removes the materialin the film 108 that is disposed on horizontal surfaces, thereby leavingspacers 109 along the sidewalls of the second backbones 116. Accordingto an embodiment, portions of the film 108 may remain above the topsurfaces of the second backbones 116, as shown in FIG. 4G. Thereafter, afirst trench etching process is used to form first trenches 141 throughthe etch-stop layer 105 and into the ILD 103. The first trench etchingprocess utilizes the spacers 109 as a mask in order to provide theproper spacing between the first trenches 141 and to be formed with thedesired width W. According to an embodiment of the invention, the widthW is less than 30 nm. An additional embodiment of the invention includesa width W that is less than 15 nm According to an embodiment, thetrenches are formed to a depth D_(T1) from the top surface of the ILD103. Embodiments of the invention include forming the first trenches 141with a depth D_(T1) between 20 nm and 60 nm Additional embodiments ofthe invention include forming the first trenches 141 to a depth D_(T1)of approximately 40 nm

Referring now to FIG. 4H a through via masking process may beimplemented according to an embodiment of the invention. A carbon hardmask 135 is disposed into the trenches 141 and above the spacers 109. Anantireflective coating 131, such as amorphous silicon, may be disposedover the carbon hardmask 135. A via mask 133, such as a photoresist, isdisposed and patterned to have a mask opening 130 formed above one ofthe first trenches 141, as shown in FIG. 4H. Referring now to FIG. 4I,the carbon hardmask 135 underneath the mask opening 130 is then etchedaway. The etching process also etches through portions of the ILD 103underneath the bottom of the first trench 141 and through the bottometch-stop layer 101 to form through via 142. Through via 142 may providea connection to layers or features below ILD 103, such as layer 170 andpad 175. While a single through via 142 is shown, embodiments may alsoinclude interconnect structures 100 with more than one through via 142.

Referring now to FIG. 4J, the remaining carbon hard mask 135,antireflective coating 131 and masking material 133 are removed.According to an embodiment metal is disposed into the first trenches 141to form the first interconnect lines 121 and into the through via 142 toform the first through via 123. Though not shown in FIG. 4J, embodimentsof the invention may also include barrier layers and/or adhesion layerssuch as, but not limited to, TaN+Ta, Ta, TaN, Ti, TiN, WN, or MnN, as iswell known to those skilled in the art. According to embodiments of theinvention, the metal may be any conductive metal used for interconnectlines, such as copper, cobalt, or tungsten. Embodiments includedisposing the first metal into the first trenches 141 and the throughvia 142 with a deposition process known in the art, such as, but notlimited to, chemical vapor deposition (CVD), atomic layer deposition(ALD), or electroplating. As shown in FIG. 4J, the top surfaces 151 ofthe first interconnects 121 have been planarized with the top surfacesof the spacers 109 in order to remove overflow material from the metaldeposition. According to an embodiment, the planarization may beperformed with a process such as chemical-mechanical planarization (CMP)or an etching process. Additional embodiments of the invention includeutilizing the planarization process to remove an upper portion of thespacers 109 and exposes the a top surfaces of the second backbones 116,as shown in FIG. 4J.

Referring now to FIG. 4K, the first interconnect lines 121 and the firstthrough via 123 are recessed back a depth R to form the recesses 143.According to embodiments of the invention, the depth R may be chosensuch that the top surfaces of the first interconnect lines 121 and thefirst through via 123 are recessed a desired distance into the ILD 103.According to an embodiment the depth R of the recesses 143 may be 10 nmor greater. According to an additional embodiment, the depth R of therecesses 143 may be 15 nm or greater. According to embodiments of theinvention that utilize copper as the interconnect metal, the etchingprocess is a wet etching process. According to embodiments of theinvention that utilize metals besides copper, such as cobalt ortungsten, the etching process may be a wet or dry etching process. Afterthe recess 143 is formed, the first interconnects 121 are a first heightH₁. Embodiments of the invention include first interconnects 121 with afirst height between 10 nm and 30 nm. According to embodiments, thefirst height H₁ may be between 15 nm and 25 nm

Referring now to FIG. 4L, first dielectric caps 125 are disposed intothe first recesses 143. According to embodiments of the invention thefirst dielectric caps may then be polished level with the top surfacesof the spacers 109, as shown in FIG. 4L. According to embodiments of theinvention, the first dielectric caps 125 may be deposited with methodssuch as chemical vapor deposition (CVD), atomic layer deposition (ALD),or physical vapor deposition (PVD). The polishing process used for thedielectric caps 125 may be a CMP process. Embodiments of the inventionmay utilize a material such as SiO_(x)C_(y)N_(z), non-conductive metaloxides, or metal nitrides for the first dielectric caps 125. Additionalembodiments of the invention may select a material for the firstdielectric caps 125 that has a high etch selectivity over the etch-stoplayer 105 and over the second dielectric caps 126 during an etchingprocess.

Referring now to FIG. 4M, the second backbones 116 are etched away.According to an embodiment, the remaining portions of the spacers 109provide a masking layer for use in etching the second trenches 144 thatare formed into portions of the ILD 103 that were previously locatedunderneath the second backbones. Embodiments of the invention includeetching the second trenches 144 to a depth D_(T2) into the ILD 103.Embodiments of the invention include depths D_(T2) that are between 10nm and 30 nm According to an embodiment of the invention, D_(T2) isapproximately 15 nm. While D_(T2) is shown as being equal to recess R,embodiments of the invention are not so limited. According to additionalembodiments, the second depth D_(T2) may be less than recess R.Alternative embodiments include a second depth D_(T2) that is greaterthan recess R, as shown in the embodiment depicted in FIG. 2B.

Referring now to FIG. 4N, a second through via patterning process isimplemented for making an electrical connection to a lower layer 170,according to an embodiment of the invention. A carbon hard mask 135 isdisposed into the second trenches 144 and above the spacers 109. Anantireflective coating 131, such as silicon, may be disposed over thecarbon hardmask 135. A via mask 133, such as a photosensitive resist orother masking materials, is disposed and patterned to have a maskopening 130 formed above one of the second trenches 144. Referring nowto FIG. 4O, the carbon hardmask 135 underneath the mask opening 130 andthe portion of the ILD 103 and the bottom etch-stop layer 101 underneaththe second trench 144 are etched away to form through via 145. Throughvia 145 may provide a connection to layers or features below ILD 103,such as layer 170 and pad 175. After the through via 145 is formed, theremaining carbon hard mask 135, antireflective coating 131 and maskingmaterial 133 are removed.

Referring now to FIG. 4P, a conductive material is disposed into secondtrenches 144 and second through via trench 145 to form the secondinterconnect lines 122 and the second through via 124. Though not shownin FIG. 4P, embodiments of the invention may also include barrier layersand/or adhesion layers such as, but not limited to, TaN+Ta, Ta, TaN, Ti,TiN, WN, or MnN, as is well known to those skilled in the art. Accordingto an embodiment, the metal disposed into the trenches may be the samemetal used to form the first interconnect lines, or it may be adifferent metal suitable for the formation of conductive interconnectlines. According to embodiments, after the deposition of the conductivematerial, the top layer is polished back to remove excess metal that mayhave been disposed outside of the second trenches 144 and through viatrench 145, with a process such as CMP or an etching process. Inembodiments of the invention portions of the spacers 109 may be polisheddown during the polishing process.

Thereafter, in FIG. 4Q the second interconnect lines 122 may be recessedbelow the etch-stop layer 105 according to an embodiment of theinvention. According to an embodiment, the recess may result in the topsurfaces 152 being disposed below the top surface of the etch stop layer105. According to an additional embodiment, the top surfaces 152 aresubstantially coplanar with the top surface of the ILD 103, or recessedbelow the top surface of the ILD 103. Embodiments include recessing thesecond interconnect lines 122 with a wet or dry etching process.According to the embodiment shown in FIG. 4Q, the height H₂ of thesecond interconnects may be the same height H₁ as the first interconnectlines 121. According to alternative embodiments the height H₂ of thesecond interconnect lines 122 may be larger or smaller than the heightH₁ of the first interconnect lines 121. Subsequent to the recessingprocess, second dielectric caps 126 may be disposed above the secondinterconnects 122 and the second through via 124. The second dielectriccaps 126 may be deposited with methods such as CVD, ALD, or PVD.Embodiments of the invention may include a material such asSiO_(x)C_(y)N_(z), non-conductive metal oxides, or metal nitrides forthe second dielectric caps 126. Additional embodiments of the inventionmay include a material for the second caps 126 that has a high etchselectivity over the etch-stop layer 105 and to the first dielectriccaps 125. Once the second dielectric caps 126 have been formed,additional dielectric material may be polished back with a chemicalmechanical planarization process or an etching process. Theplanarization process may also polish away the remaining portions of thespacers 109 in order to leave only the top surface of the etch-stoplayer 105 and the top surfaces of the first and second caps 125, 126exposed.

According to an additional embodiment, the spacers 109 may be completelypolished back during the polishing process used to remove the excessconductive material disposed in the second trenches to form the secondinterconnect lines 122. Thereafter, the second interconnect lines may berecessed and filled with a dielectric material to form the seconddielectric caps 126 as described above.

Alternative embodiments may forego recessing the second interconnectlines 122 when etch selectivity is not needed to make contacts toindividual interconnect lines. For example, etch selectivity may not beneeded when the pitch between interconnect lines is large enough thatmisaligned contact openings will not overlap a neighboring interconnectline. According to such embodiments, an etch-stop layer may be disposedover the top surface of the second interconnect lines 122 and the topsurface of the exposed etchstop layer 105.

According to an additional embodiment of the invention, the first andsecond interconnect lines 121, 122 may be formed in reverse order (i.e.,the recessed first interconnect lines 121 may be formed subsequent tothe formation of the second interconnect lines 122). Certain embodimentsof the invention in which the second interconnect lines 122 are formedprior to the formation of the first interconnect lines 121 may bemanufactured according to the processes described with respect to FIGS.5A-5G. A method of forming the low capacitance interconnect structure100 according to this embodiment of the invention comprises initialprocessing similar to those described with respect to FIGS. 4A-4F, andtherefore will not be repeated here. Accordingly, FIG. 5A illustratesprocessing of the interconnect structure 100 following the formation ofthe spacer film 108 shown in FIG. 4F. Additionally, though not shown inFIGS. 5A-5F, those skilled in the art will recognize that first andsecond through vias may also be included in an interconnect structure100 formed in accordance with embodiments of the invention. According tosuch embodiments, masking and etching processes substantially similar tothose described with respect to FIGS. 4H-4I, and 4N-4O may beimplemented in order to produce through vias 121 and 123 as desired.

Referring now to FIG. 5A, a spacer etch is implemented to form spacers109 that are substantially similar to the spacers 109 formed in FIG. 4G.Embodiments of the invention then utilize a second etching process inorder to form the second trenches 144. Embodiments of the inventioninclude etching the second trenches 144 to a depth D_(T2) into the ILD103. Embodiments of the invention include depths D_(T2) that are between10 nm and 30 nm According to an embodiment of the invention, D_(T2) isapproximately 15 nm.

After the second trenches 144 have been formed, the trenches are filledwith a conductive material to form the second interconnect lines 122, asshown in FIG. 5B. According to embodiments of the invention, the metalmay be any conductive metal used for interconnect lines, such as copper,cobalt, or tungsten. Embodiments include disposing the metal into thesecond trenches 144 with a deposition process known in the art, such asCVD. In an embodiment, the overburden is polished back with a polishingprocess, such as CMP or an etching process. Additional embodiments ofthe invention utilize the planarization process to remove an upperportion of the spacers 109 and expose top surfaces of the secondbackbones 116.

Referring now to FIG. 5C, the second interconnect lines 122 are recessedbelow the etch-stop layer 105. According to an embodiment, the topsurfaces 142 of the second interconnect lines 122 are recessed such thatthey are substantially coplanar with the top surface of the ILD 103.According to additional embodiments, the top surfaces 142 secondinterconnect lines 122 may be recessed below the top surface of the ILD103. Embodiments include recessing the second interconnect lines 122with a wet or dry etching process. Subsequent to the recessing process,second dielectric caps 126 may be disposed above the secondinterconnects 122. The second dielectric caps 126 may be deposited withmethods such as CVD, ALD, or PVD. Embodiments of the invention havesecond dielectric caps 126 that are made of a material such asSiO_(x)C_(y)N_(z), metal oxides, or metal nitrides. Additionalembodiments of the invention may have second dielectric caps 126 thathave a high selectivity over the etch-stop layer 105 and to the firstdielectric caps 125 during an etching process. Once the seconddielectric caps 126 have been formed, additional dielectric material maybe polished back. According to an embodiment, the second dielectric caps126 are polished back such that they are substantially coplanar with thetop surfaces of the spacers 109. According to an embodiment thepolishing process may be implement with a CMP process or an etchingprocess.

Referring now to FIG. 5D the second backbones 116 are etched away andthe first trenches 141 are formed into the ILD 103 with a trench etchingprocess. According to an embodiment, the trenches are formed to a depthD_(n). Embodiments of the invention have first trenches 141 with a depthD_(T1) between 20 nm and 60 nm Additional embodiments of the inventioninclude forming the first trenches 141 with a depth D_(T1) ofapproximately 40 nm. First trenches 141 are then filled with aconductive material to form the first interconnect lines 121, as shownin FIG. 5E. According to embodiments of the invention, the conductivematerial may be any conductive metal used for interconnect lines, suchas copper, cobalt, or tungsten. Embodiments include disposing the firstmetal into the first trenches with a deposition process known in theart, such as CVD. In an embodiment, the overburden is polished back witha polishing process, such as CMP or an etching process.

Thereafter the first interconnect lines 121 may be recessed a depth Rinto the ILD 103, as shown in FIG. 5F. Embodiments may use a wet or dryetching process to recess the first interconnect lines 121. Firstdielectric caps 125 may then be disposed above the recessed firstinterconnect lines 121. According to embodiments, the first dielectriccaps may be deposited with methods such as CVD, ALD, or PVD. Embodimentsof the invention have first dielectric caps 125 that are made of amaterial such as SiO_(x)C_(y)N_(z), non-conductive metal oxides, ormetal nitrides for the first dielectric caps 125. Additional embodimentsof the invention have first dielectric caps 125 that have a highselectivity over the etch-stop layer 105 and to the second dielectriccaps 126 during an etching process. After the first dielectric caps 125have been formed, additional dielectric material may be polished backwith a CMP process or an etching process, such that the first dielectriccaps are substantially coplanar with the top surface of the spacers 109.According to an embodiment, the polishing process used to remove theexcess dielectric material may also remove the remaining portions of thespacers 109.

FIG. 6 illustrates a computing device 600 in accordance with oneimplementation of the invention. The computing device 600 houses a board602. The board 602 may include a number of components, including but notlimited to a processor 604 and at least one communication chip 606. Theprocessor 604 is physically and electrically coupled to the board 602.In some implementations the at least one communication chip 606 is alsophysically and electrically coupled to the board 602. In furtherimplementations, the communication chip 606 is part of the processor604.

Depending on its applications, computing device 600 may include othercomponents that may or may not be physically and electrically coupled tothe board 602. These other components include, but are not limited to,volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flashmemory, a graphics processor, a digital signal processor, a cryptoprocessor, a chipset, an antenna, a display, a touchscreen display, atouchscreen controller, a battery, an audio codec, a video codec, apower amplifier, a global positioning system (GPS) device, a compass, anaccelerometer, a gyroscope, a speaker, a camera, and a mass storagedevice (such as hard disk drive, compact disk (CD), digital versatiledisk (DVD), and so forth).

The communication chip 606 enables wireless communications for thetransfer of data to and from the computing device 600. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. The communication chip 606 may implement anyof a number of wireless standards or protocols, including but notlimited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE,GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well asany other wireless protocols that are designated as 3G, 4G, 5G, andbeyond. The computing device 600 may include a plurality ofcommunication chips 606. For instance, a first communication chip 606may be dedicated to shorter range wireless communications such as Wi-Fiand Bluetooth and a second communication chip 606 may be dedicated tolonger range wireless communications such as GPS, EDGE, GPRS, CDMA,WiMAX, LTE, Ev-DO, and others.

The processor 604 of the computing device 600 includes an integratedcircuit die packaged within the processor 604. In some implementationsof the invention, the integrated circuit die of the processor includesone or more devices, such as devices that include a low capacitanceinterconnect structure built in accordance with implementations of theinvention. The term “processor” may refer to any device or portion of adevice that processes electronic data from registers and/or memory totransform that electronic data into other electronic data that may bestored in registers and/or memory.

The communication chip 606 also includes an integrated circuit diepackaged within the communication chip 606. In accordance with anotherimplementation of the invention, the integrated circuit die of thecommunication chip includes one or more devices, such as devicesincluding a low capacitance interconnect structure built in accordancewith implementations of the invention.

In further implementations, another component housed within thecomputing device 600 may contain an integrated circuit die that includesone or more devices, such as devices including a low capacitanceinterconnect structure built in accordance with implementations of theinvention.

In various implementations, the computing device 600 may be a laptop, anetbook, a notebook, an ultrabook, a smartphone, a tablet, a personaldigital assistant (PDA), an ultra mobile PC, a mobile phone, a desktopcomputer, a server, a printer, a scanner, a monitor, a set-top box, anentertainment control unit, a digital camera, a portable music player,or a digital video recorder. In further implementations, the computingdevice 600 may be any other electronic device that processes data.

Embodiments of the invention include, an interconnect structurecomprising, an interlayer dielectric (ILD), one or more firstinterconnect lines disposed in the ILD, wherein a first dielectric capis disposed above a top surface of each of the first interconnect lines,and one or more second interconnect lines disposed into the ILD in analternating pattern with the first interconnect lines, wherein a seconddielectric cap is disposed above a top surface of each of the secondinterconnect lines, and wherein the top surfaces of the firstinterconnect lines are recessed into the ILD deeper than the topsurfaces of the second interconnect lines. An additional embodimentincludes and interconnect structure wherein the first dielectric capsare a different material than the second dielectric caps. An additionalembodiment includes an interconnect structure wherein the firstdielectric caps are resistant to an etching process that is selective tothe second dielectric caps. An additional embodiment includes aninterconnect structure, wherein the first dielectric caps and the seconddielectric caps are resistant to an etching process that is selective toan etch-stop layer disposed above the ILD. An additional embodimentincludes an interconnect structure wherein the top surfaces of the firstinterconnect lines are disposed deeper into the ILD than bottom surfacesof the second interconnect lines. An additional embodiment includes aninterconnect structure, wherein bottom surfaces of the secondinterconnect lines are disposed deeper into the ILD than the topsurfaces of the first interconnect lines. An additional embodimentincludes an interconnect structure further comprising one or more firstthrough vias formed through the ILD, wherein top surfaces of the firstthrough vias are recessed the same depth into the ILD as the topsurfaces of the first interconnect lines, and a first dielectric cap isdisposed on the top surfaces of the first through vias. An additionalembodiment includes an interconnect structure further comprising one ormore second through vias formed through the ILD, wherein a seconddielectric cap is disposed on the top surfaces of the second throughvias. An additional embodiment includes an interconnect structurewherein the first and second caps are a SiOxCyNz material, a metal oxidematerial, or a metal nitride material. An additional embodiment includesan interconnect structure, wherein the first interconnect lines arespaced less than 25 nm from the second interconnect lines. An additionalembodiment includes an interconnect structure, wherein the firstinterconnect lines have a first height and the second interconnect lineshave a second height. An additional embodiment includes an interconnectstructure, wherein the first height is larger than the second height.

An embodiment of the invention includes, a method of forminginterconnects comprising, forming one or more first trenches into aninterlayer dielectric (ILD), disposing a first metal into the one ormore first trenches to form first interconnect lines, forming firstdielectric caps above top surfaces of the first interconnect lines,forming one or more second trenches into the ILD in an alternatingpattern with the first trenches, disposing a second metal into the oneor more second trenches to form second interconnect lines, wherein thetop surfaces of the first interconnect lines are recessed deeper intothe ILD than top surfaces of the second interconnect lines, and formingsecond dielectric caps on the top surface of the second interconnects.An additional embodiment includes a method of forming interconnectswherein forming the first trenches comprises forming a hardmask above anetch-stop layer disposed over the ILD, forming spacers on the sidewallsof the hardmask, wherein a portion of the etch-stop layer remainsexposed between the spacers, and etching through the exposed portions ofthe etch-stop layer and into the ILD underneath the exposed portions ofthe etch-stop layer. An additional embodiment includes a method offorming interconnects wherein forming the second trench comprisesetching through the hardmask, and etching through portions of theetch-stop layer and into the ILD that were previously disposedunderneath the hardmask. An additional embodiment includes a method offorming interconnects further comprising etching through portions of theILD disposed underneath one or more of the first trenches prior todisposing the first metal into the first trenches. An additionalembodiment includes a method of forming interconnects, furthercomprising etching through portions of the ILD underneath one or more ofthe second trenches prior to disposing the second metal into the secondtrenches. An additional embodiment includes a method of forminginterconnects wherein the first dielectric caps are resistant to anetching process that is selective to the second dielectric caps. Anadditional embodiment includes a method of forming interconnects whereinthe top surfaces of the first interconnect lines are disposed deeperinto the ILD than below bottom surfaces of the second interconnectlines. An additional embodiment includes a method of forminginterconnects wherein bottom surfaces of the second interconnect linesare disposed deeper into the ILD than the top surfaces of the firstinterconnect lines. An additional embodiment includes a method offorming interconnects wherein the first interconnect lines are spacedapart from the second interconnect lines by less than 25 nm. Anadditional embodiment includes a method of forming interconnects whereinthe first and second caps are a SiOxCyNz material, a metal oxidematerial, or a metal nitride material.

An embodiment of the invention includes a method of forminginterconnects comprising, forming and etch-stop layer above aninterlayer dielectric (ILD), forming a patterned hardmask above theetch-stop layer, forming a spacer layer over the surfaces of thepatterned hardmask and the exposed portions of the etch-stop layer,etching through the spacer layer to form hardmask spacers along thesidewalls of the patterned hardmask, etching through the etch-stop layerand the dielectric layer to form first trenches defined by the hardmaskspacers, disposing a first metal into the first trenches to form firstinterconnect lines in the first trenches, disposing a first cap aboveeach of the first interconnect lines, etching through the patternedhardmask, and the portions of the etch-stop layer and the ILD underneaththe patterned hardmask to form second trenches, disposing a second metalinto the second trenches to form second interconnect lines in the secondtrenches, wherein the top surfaces of the first interconnect lines arerecessed deeper into the ILD than the top surfaces of the secondinterconnect lines, disposing a second dielectric cap above each of thesecond interconnects. An additional embodiment includes a method offorming interconnects wherein the top surfaces of the first interconnectlines are recessed below the bottom surfaces of the second interconnectlines. An additional embodiment includes a method of forminginterconnects wherein bottom surfaces of the second interconnect linesare disposed deeper into the ILD than the top surfaces of the firstinterconnect lines.

What is claimed is:
 1. An interconnect structure comprising: aninterlayer dielectric (ILD); one or more first interconnect linesdisposed in the ILD, wherein a first dielectric cap is disposed above atop surface of each of the first interconnect lines; and one or moresecond interconnect lines disposed into the ILD in an alternatingpattern with the first interconnect lines, wherein a second dielectriccap is disposed above a top surface of each of the second interconnectlines, and wherein the top surfaces of the first interconnect lines arerecessed into the ILD deeper than the top surfaces of the secondinterconnect lines.
 2. The interconnect structure of claim 1, whereinthe first dielectric caps are a different material than the seconddielectric caps.
 3. The interconnect structure of claim 2, wherein thefirst dielectric caps are resistant to an etching process that isselective to the second dielectric caps.
 4. The interconnect structureof claim 3, wherein the first dielectric caps and the second dielectriccaps are resistant to an etching process that is selective to anetch-stop layer disposed above the ILD.
 5. The interconnect structure ofclaim 1, wherein the top surfaces of the first interconnect lines aredisposed deeper into the ILD than bottom surfaces of the secondinterconnect lines.
 6. The interconnect structure of claim 1, whereinbottom surfaces of the second interconnect lines are disposed deeperinto the ILD than the top surfaces of the first interconnect lines. 7.The interconnect structure of claim 1, further comprising one or morefirst through vias formed through the ILD, wherein top surfaces of thefirst through vias are recessed the same depth into the ILD as the topsurfaces of the first interconnect lines, and a first dielectric cap isdisposed on the top surfaces of the first through vias.
 8. Theinterconnect structure of claim 1, further comprising one or more secondthrough vias formed through the ILD, wherein a second dielectric cap isdisposed on the top surfaces of the second through vias.
 9. Theinterconnect structure of claim 1, wherein the first and second caps area SiO_(x)C_(y)N_(z) material, a metal oxide material, or a metal nitridematerial.
 10. The interconnect structure of claim 1, wherein the firstinterconnect lines are spaced less than 25 nm from the secondinterconnect lines.
 11. The interconnect structure of claim 1, whereinthe first interconnect lines have a first height and the secondinterconnect lines have a second height.
 12. The interconnect structureof claim 11, wherein the first height is larger than the second height.13. A method of forming interconnects comprising: forming one or morefirst trenches into an interlayer dielectric (ILD); disposing a firstmetal into the one or more first trenches to form first interconnectlines; forming first dielectric caps above top surfaces of the firstinterconnect lines; forming one or more second trenches into the ILD inan alternating pattern with the first trenches; disposing a second metalinto the one or more second trenches to form second interconnect lines,wherein the top surfaces of the first interconnect lines are recesseddeeper into the ILD than top surfaces of the second interconnect lines;and forming second dielectric caps on the top surface of the secondinterconnects.
 14. The method of claim 13, wherein forming the firsttrenches comprises forming a hardmask above an etch-stop layer disposedover the ILD, forming spacers on the sidewalls of the hardmask, whereina portion of the etch-stop layer remains exposed between the spacers,and etching through the exposed portions of the etch-stop layer and intothe ILD underneath the exposed portions of the etch-stop layer.
 15. Themethod of claim 14, wherein forming the second trench comprises etchingthrough the hardmask, and etching through portions of the etch-stoplayer and into the ILD that were previously disposed underneath thehardmask.
 16. The method of claim 13, further comprising etching throughportions of the ILD disposed underneath one or more of the firsttrenches prior to disposing the first metal into the first trenches. 17.The method of claim 13, further comprising etching through portions ofthe ILD underneath one or more of the second trenches prior to disposingthe second metal into the second trenches.
 18. The method of claim 13,wherein the first dielectric caps are resistant to an etching processthat is selective to the second dielectric caps.
 19. The method of claim13, wherein the top surfaces of the first interconnect lines aredisposed deeper into the ILD than below bottom surfaces of the secondinterconnect lines.
 20. The interconnect structure of claim 13, whereinbottom surfaces of the second interconnect lines are disposed deeperinto the ILD than the top surfaces of the first interconnect lines. 21.The interconnect structure of claim 13, wherein the first interconnectlines are spaced apart from the second interconnect lines by less than25 nm.
 22. The interconnect structure of claim 13, wherein the first andsecond caps are a SiO_(x)C_(y)N_(z) material, a metal oxide material, ora metal nitride material.
 23. A method of forming interconnectscomprising: forming and etch-stop layer above an interlayer dielectric(ILD); forming a patterned hardmask above the etch-stop layer; forming aspacer layer over the surfaces of the patterned hardmask and the exposedportions of the etch-stop layer; etching through the spacer layer toform hardmask spacers along the sidewalls of the patterned hardmask;etching through the etch-stop layer and the dielectric layer to formfirst trenches defined by the hardmask spacers; disposing a first metalinto the first trenches to form first interconnect lines in the firsttrenches; disposing a first cap above each of the first interconnectlines; etching through the patterned hardmask, and the portions of theetch-stop layer and the ILD underneath the patterned hardmask to formsecond trenches; disposing a second metal into the second trenches toform second interconnect lines in the second trenches, wherein the topsurfaces of the first interconnect lines are recessed deeper into theILD than the top surfaces of the second interconnect lines; anddisposing a second dielectric cap above each of the secondinterconnects.
 24. The method of claim 23, wherein the top surfaces ofthe first interconnect lines are recessed below the bottom surfaces ofthe second interconnect lines.
 25. The interconnect structure of claim23, wherein bottom surfaces of the second interconnect lines aredisposed deeper into the ILD than the top surfaces of the firstinterconnect lines.